The present invention relates to novel substituted quinazolinones useful as pharmaceutical agents, to methods for their production, to pharmaceutical compositions which include these compounds and a pharmaceutically acceptable carrier, and to a pharmaceutical method of treatment. More particularly, the novel compounds of the present invention inhibit the enzyme thymidylate synthase (TS) thus inhibiting the growth of malignant neoplasms in mammals.
Most traditional antifolate anticancer drugs act by inhibiting the enzyme dihydrofolate reductase (DHFR). Inhibition of DHFR has been associated clinically with the development of resistance by overproduction of DHFR. In such cases TS may become the rate limiting enzyme for continued cell growth. It has been demonstrated experimentally and clinically that inhibition of TS is a viable approach for cancer chemotherapy.
TS is the enzyme that mediates the last step in the de novo synthesis of thymidylate required for deoxyribonucleic acid (DNA). Several quinazolinone folic acid analogs have been identified as inhibitors of TS. UK Patent Application No. 2,065,653A describes a series of anti-cancer quinazoline derivatives. One analog in this series, N-(4(N-((2-amino-4-hydroxy-6-quinazolinyl)methyl)prop-2-ynylamino)benzoyl) -L-glutamic acid (CB 3717), a selective, tight binding TS inhibitor was tested in Phase I clinical trials. Minor and partial clinical responses were reported for patients with ovarian and breast cancer. However, nondose related liver toxicity and dose limiting kidney toxicity due in part to the poor solubility of this 2-amino folate analog led to the development of second generation compounds which are devoid of this substituent. UK Patent Application No. 2,175,903A describes a related series of anti-cancer quinazolines. These 2-des amino derivatives are somewhat weaker inhibitors of TS than the 2-amino derivatives but are more selective for TS than DHFR. They are reported to retain sufficient activity to be useful anticancer agents devoid of both hepatic and renal toxicity in experimental models. European patent application 0239362 discloses additional 2-substituted quinazolines related to CB 3717.
To date, all quinazolinone inhibitors of TS were thought to require the classical glutamic acid side chain, polyglutamates thereof, or related amino acid residues for enzyme inhibitory activity and therapeutic efficacy. For example, Jones et al, Journal of Medicinal Chemistry, Vol. 29, pp. 1114-1118 (1986) reported that removal of the glutamate residue (formula A; R=OH) decreased TS inhibition by 84-fold over the classical antifolate analog ##STR1## thus emphasizing the importance of an amino acid residue for strong binding to the enzyme.
Moreover, resistance to classical antifolates via impairment of the reduced folate carrier system is common and may be reasonably anticipated for the classical TS inhibitors as well. However, lipophilic antifolates, which lack the classical glutamic acid or related amino acid side chain, such as the DHFR inhibitor trimetrexate have been shown to circumvent the impaired transport seen in cells made resistant to the classical DHFR inhibitor methotrexate. Lipophilic antifolates with enzyme target other than DHFR, such as TS, might circumvent the impaired transport type of resistance often associated with classical glutamate antifolates. Therefore, we have found unexpectedly that a lipophilic nonclassical series of substituted quinazolinones without the classical amino acid residue has potent selective inhibitory activity against TS.